The subject disclosure is directed to fluid filtration, and more particularly, to a bag-type filter assembly having two concentric circumferentially pleated media sleeves defining an annular passage therebetween, which receives fluid for filtration.
Bag-type filter systems for fluid filtration are well known in the art. These systems typically include a cylindrical housing, which is closed at one end and has a removable cover at the opposed end. An inlet conduit delivers fluid to be filtered into the housing and an outlet conduit removes filtered fluid from the housing.
Replaceable bag filters are disposed within the housing in order to filter fluids delivered thereto. Typically, bag filters include filter media having an open upper end and a closed bottom. The filter bag is supported within an open mesh basket or cage, which is typically suspended within the housing. The basket is intended to support the media of the filter bag to prevent it from bursting as the bag fills with liquid.
There are several disadvantages associated with existing bag-type filters. One such disadvantage is that filter bags have a large hold-up volume. Thus, removal of a used filter bag is quite difficult, because it can be relatively heavy. A full filter bag could weigh as much as thirty pounds and it may contain hazardous substances, adding to the difficulty of removal. To remedy this situation, evacuation balloons have been used to reduce the hold-up volume prior to the removal of a used bag. However, these balloons are often cumbersome to handle.
Another disadvantage associated with existing bag filters is that they provide a limited amount of effective filtration area. Efforts to increase the effective filtration area of existing bag filter have been limited because of the industry standardization of basket sizes. That is, filter bags are typically available it two distinct sizes: (#1) 7″ diameter×16″ long; and (#2) 7″ diameter ×32″ long. Consequently, any increase in effective filtration area is limited by the requirement that the outer diameter of the filter cannot be altered.
There have been a number of efforts to design bag filters to minimize hold-up volume and maximize the effective area for filtration. For example, U.S. Pat. No. 4,081,379 discloses an annular filter bag that provides more available surface area than a conventional filter bag. U.S. Pat. Nos. 4,863,602 and 4,877,526 disclose a bag filter with increased surface area that includes multiple wrapped layers of melt-blown media with a flexible transport layer in between. The Hayward Lofclear 500 Series bag filter provides increased surface area by folding a pre-filter layer, which is wrapped by final filtration layers. For the most part, these prior art efforts have fallen short.
A particularly useful bag-type filter assembly is disclosed in U.S. Pat. Nos. 6,030,531 and 6,238,560. In this unique filter assembly, effective surface area is increased by providing two concentric media sleeves connected at one end to an open inlet cap and at the opposed end to a closed end cap. The dual sleeve configuration also minimizes the hold-up volume of fluid remaining in the filter element after use, making it easier to remove from the filter basket/housing.
Over the years, the design of cylindrical pleated filter cartridges has involved similar efforts to maximize the amount of filter media or surface area that may be fit into a filter cartridge having a given outer diameter. In a standard radially pleated filter cartridge, the number of pleats that can be packed about the cartridge core limits the amount of filter media that may be packed into the cartridge. Consequently, there is a substantial amount of empty space between adjacent pleats at the outer periphery of the filter element.
A spiral pleated filter element is comparable to a standard radially pleated filter element in that it includes a plurality of longitudinal pleats disposed in a cylindrical configuration. In a spiral-pleated filter, however, the ends of the pleats are rolled over to minimize the spacing between adjacent pleat surfaces near an outer diameter of the filter element. In this case, the pleat height is substantially greater than the distance between the outer periphery of the cartridge core and the inner periphery of the cartridge cage. Consequently, in a spiral-pleated filter, the pleats at the outer periphery occupy the excess volume that would normally represent empty space in a radially pleated filter element. This provides increased filter surface area as compared to a standard radial pleat configuration.
It would be beneficial to employ techniques used to enhance effective surface area in pleated filter cartridges to bag-type filters. This would provide increased filter life, lower pressure drop and lower the operating costs for the customer.